1. Field of the Invention
The present invention relates to the field of computer video systems, and more particularly to calibrating a local raster to an external remote raster.
2. Description of the Related Art
Modern data processing systems generally provide visual output by way of such output devices as cathode ray tubes or liquid crystal displays. The performance of such systems can be enhanced when the visual display receives information from more than one source, and overlays the information received from a first source with the information received from a second source. For example, a first video subsystem may provide background graphics, such as windows, on a rasterized computer display. A separate video subsystem, typically residing on a video card, may provide video information, such as a photographic image, which overlays the inside of the window to serve as the contents of the window.
When operating in native mode, most conventional video subsystems generate static images, such as document text. Recent technological advancements have made possible video cards for generating motion video for applications such as video conferencing. It is desirable to provide the capability to install such an advanced video card in a host computer system that employs a preexisting video (typically graphics) subsystem. However, to achieve compatibility between the new video subsystem and the preexisting graphics subsystem, a number of the motion video subsystem raster parameters must be calibrated to the graphics raster so that video images produced by the video card are aligned and synchronized with graphics generated by the graphics subsystem. Conventional systems require the user to visually align a test pattern generated by the local video subsystem with a test pattern generated by the remote graphics subsystem. It is desired to find a less cumbersome means for calibrating the local raster to the remote raster.